Producing vacuums



i ITED- PATENT- OFFICE HUGE S. COOPER, OF CLEVELAND, OHIO, ASSIGNOR TO KEME'I' LABORATORIES COM- PANY, INC., A CORPORATION OF NEW YORK rnonucme vacuums No Drawing.

The invention relates to the production of high vacuums for any purpose, but particularly in hot cathode devices such as the tubes or valves used in radio communication.

In the prevailing practice, electron tubes are evacuated by pumping to a convenient degree of exhaustion, and then subjecting the residual gases to the action of a clean-up agent, which, it is believed, fixes the residual 1o gases by both chemical and physical action.

Magnesium is the usual clean-up agent, but other substances, for example the metals barium and strontium, give higher vacuums under certain conditions. In attempting to substitute these latter metals for magnesium, dificulties are encountered because the metals require higher temperatures than magnesium to cause them to flash, that is to begin to react rapidly with the gases present.

The usual method of flashing the clean-up agent is to introduce it in solid form into the envelope, then seal the envelope either temporarily or permanently, and then bring the envelope into the field of a coil in which highfrequency alternating current flows; and it is found that the equipment available, designed for flashing magnesium. mav not have enough power to flash barium and other very active agents within the time allotted to this operation in the semi-automatic machines used in making thermionic tubes. In the present large-scale manufacture of tubes, it is of course desirable to carry out each operation as rapidly as possible.

An object of the invention is to facilitate the flashing of such agents as barium and strontium, and to adapt them to the equip ment and schedules now employed with magnesium. This is accomplished by alloyingthe barium or strontium with magnesium in such proportions as to produce stable alloys containing effective quantities of the former metals, powdering the resulting brittle alloys and compressing the powders which are selfbonding, into pellets of the desired size.

The invention will be described more particularly hereinafter by reference to alloys of barium with magnesium.

Magnesium and barium alloy in all proportions, and certain of the alloys have been Application filed December 81, 1929. Serial No. 417,825.

found to be relatively stable in the air. It will be recognized that it is impossible to differentiate sharply between compositions which are stable in air and those which are not, especially since the action of the air varies with its humidity, but it may be stated that stability falls off with increasing barium content, and that alloys containing up to about 30% of barium are fairly stable in air. Alloys which are unstable in air are also useful, but they must be protected from prolonged exposure to air. As little as 10% of magnesium alloyed with barium will substantially lower the energy requirements for flashing the getter, while as little as 5% of barium increases the thoroughness of the clean-up. The alloys of barium and magnesium which are most suitable for my purose have little ductility as a rule and cannot e readily drawn into wire or other attenu ated forms. Some of the alloys are quite brittle. This property does not constitute a serious objection as I have found that the powdered alloys have self bonding properties and can be readily agglomerated, as by pressing into pellets. Appropriate binders may be used if desired.

The pellets of the powdered alloy as stated are sta le in air and readily may be handled without objectionable contamination by vaporizable impurities.

Barium-magnesium alloys can be easily repared by fusing the ingredients in an inert atmosphere, such as argon or helium, in

a suitable vessel, for example a crucible of commercially carbon-free iron. For pure barium I may substitute any barium alloy which is free from substances detrimental to a gas clean-up agent. Similarly, strontium 

